The murine teratocarcinoma is capable of differentiating into tissues of all three germ layers. We have developed an in vitro model of this tumor and plan to study the process of differentiation and the cell types generated from this system. To characterize the cell system we will outline cytogenetic analysis and DNA content (FMF) measurements to determine the relationship of chromosome patterns to differentiation. Time-lapse cinemicrography will be utilized to follow the life history of stem cells and differentiated cells. Analysis of isozyme patterns and cAMP levels of stem cells and differentiated cells will be compared. Further experiments are proposed to analyze the response of teratocarcinoma cells to polyoma virus. These studies will include the analysis for interferon, blocking factors, characterization of virus produced and presence of viral DNA or viral RNA. These studies will be useful in defining the unique carrier state which is dependent upon the differentiative state of the cells. Analysis of the production of polyploid cells and the relationship of these cells to transformation with SV40 is proposed following separation of these cells. DNA synthesis and cell cycle distribution of cells transformed with SV40 temperature sensitive (Ts) mutants will be compared following temperature shifts (33 degrees yields 40 degrees C). Ultrastructural analysis of infected cells will be compared with peroxidase-labeled Fab fragments to antibody to SV40 T antigen and the V antigens.